In my previous Canadian patent application Ser. No. 2,086,060 entitled "Broadband Directional Coupler Using Cables", I describe the construction of a broadband directional coupler formed by using commercially available coaxial cables which are semi-rigid and wherein I strip the shielding sleeve to expose a section of the inner cable which I then couple to another like section of cable to thereby form a coupler. This technique has many advantages over prior art techniques, such as being inexpensive to fabricate, it eliminates the need to produce expensive machined metal shielding housings, and provides flexibility in that the coupler can be shaped to many desired forms to save space, or to fit in a predetermined restricted space.
These advantages that I achieved with my broadband directional coupler led to further research and development in the use of flexible, semi-flexible or rigid coaxial cables, and I have now developed the coaxial cable technology to construct other components, such as filters, or to use the coaxial cable as the base for the construction of electronic circuits wherein I incorporate electronic components or chips directly coupled to the inner conductor in a window region of the cable. I have also developed economical means of providing housings about the strip regions or in the end portion of one or more of these cables wherein electronic circuits can be housed and shielded.
The fabrication of filters using classical technologies, such as a printed circuit board having lumped LC components, micro-strip, strip-line, etc., is known and it necessitates the use of various fabrication techniques and element sources. Such a construction is, for example, described in U.S. Pat. No. 4,835,499 issued May 30, 1989, entitled "Voltage Tunable Bandpass Filter". That patent describes a bandpass filter which is formed from a plurality of parallel resonators formed of micro-strips which are fitted on a circuit board and spaced with great accuracy. An advantage of such construction is that the resonators are simpler and less expensive to produce, but still occupy the space of the printed circuit board on which other components, such as tuning diodes and capacitors are coupled to the resonators. Such construction does not offer flexibility, nor is it useful in saving space, nor can it be designed to fit in a small predetermined area. These circuit boards also need to be shielded and must therefore be mounted in a shielded housing.